The howling margin of an acoustic system that includes microphones and speakers such as installed in a concert hall needs to be obtained in some cases. Such a howling margin has been heretofore measured by the following method.
Ordinary acoustic systems are equipped with a means for gain control. When an acoustic system is brought into a condition appropriate for use in a concert held in a concert hall for instance, the gain of the acoustic system is also set to a value appropriate for use in the concert.
A measurement of the howling margin of the acoustic system thus adjusted and set is generally made by a gain controlling means provided for the acoustic system. As the gain controlling means used for the measurement in this case, an output fader for a mixing console placed between a microphone and a speaker is commonly used.
Using, as a reference level, the condition of the gain controlling means of the acoustic system adjusted and set a concert, the operator controls the gain of the gain controlling means so as to gradually increase from the reference level. Until the acoustic system starts howling, the gain of the gain controlling means is increased by the operator. At the time when the acoustic system starts howling, the speaker makes sound waves having a specified frequency (howling frequency). The operator aurally checks this sound thereby knowing that generation of howling has started. Then, he obtains a howling margin from how much the gain of the gain controlling means when howling starts exceeds the reference level. For instance, if the reference level of the fader that serves as the gain controlling means is “−10 dB” and the level of the fader when the acoustic system starts howling is “−5 dB”, the howling margin is “5 dB”.
In the above method, however, a start of howling is determined depending on the sense of hearing of the operator. Therefore, a good operator's skill is required for making an accurate howling measurement. If an inexperienced operator measures a howling margin with the above method, the operator may fail in catching a howling sound while howling being generated and recklessly leave the howling to increase. In addition, the operator judges the level of the fader by reading the calibration mark provided beside the fader. Therefore, it is difficult for the operator to precisely read the calibration mark and therefore difficult to make an accurate measurement of a howling margin.
Further, such howling margin measurement dependent upon the skill of the operator is an obstacle to automatization of adjustment/setting of an acoustic system.
Although Japanese Unexamined Published Patent Application No. 09-247787 (Page 4, Paragraph No. 0024) makes mention of howling margin measurement, it does not concretely teach a system configuration nor method for making such a measurement.